Measurements of Polymethyl Methacrylate Diffusion Flames in Von Karman Swirling Flows

Abstract

In 1921 an analysis by von Karman demonstrated that viscous pumping action occurs when a flat disk is rotated in a fluid of semi-infinite extent. The rotation draws material inward normal to the disk, forcing it radially outward, thereby causing a swirling motion. A similarity exists near the disk, in the vicinity of the centerline, such that the radial and tangential velocity components are propor-tionalto the radius, while all other flow properties depend only on the distance normal to the disk. If the disk is a fuel and the ambient fluid is an oxidizing gas, then a flat laminar diffusion flame parallel to the disk can be established in the swirling flow drawn in. Theoretical descriptions of such flames have been developed previously, and some experiments have been performed, notably for disks of polymethyl methacrylate (PMMA) in air. The present contribution provides quantitative measurements of burning rates and flame stand-off distances for such rotating disks and demonstrates that time-dependent heating of the fuel is important under these conditions, while nearly steady-state conditions apply in the gas. The fully steady-state solutions that have been published would apply to PMMA only for combustion in oxygen-enriched atmospheres for the sample sizes and rotational rates of the present experiments.